Technical Abstract:
Pb contamination of urban soils and its strong association with elevated blood Pb concentrations, especially in children, has raised concerns about whether gardens should be recommended for urban areas. Reliable evaluation of the potential hazard to the public from exposure to urban garden soils greatly depends upon the bioavailability of Pb in ingested soil. Several researchers have shown that in vivo soil Pb bioavailability trials can be replaced with in vitro or bioaccessibility tests to save costs and time. However, present bioaccessibility methods are expensive and laborious. Thus, there is a dire need of an easier and low cost bioaccessibility test method that could be widely adopted by agricultural and environmental laboratories. The authors have developed a new soil Pb bioaccessibility extraction test method (extraction of <2 mm soil with 0.4 molar glycine solution adjusted to pH 2.5, at room temperature and shaking for 15 minutes @ 100 rpm) which is 10-20 times less expensive than previous established methods. The method not only shows a high correlation with results from feeding Joplin (Mo) control and remediated smelter contaminated soils to human and rats, but also explores new findings from Pb rich urban gardens. The method revealed that fractional bioaccessibility (compared to total) of Pb in urban garden soils is only 2-9%, far lower than the presumed 50% by US-EPA. EXAFS examination of Pb speciation in the urban garden soils will also be reported. These findings suggest that urban gardening has much lower potential for Pb risk than EPA is currently assuming, and that authorities could recommend urban gardening more freely than previously feared. The findings also support revised recommendations from US-EPA for Pb contaminated urban gardens and superfund sites. The findings have broader implications for other developed and developing countries due to low costs and easier adoptability by all soil testing laboratories.